1. Field of the Invention
The present invention relates to an original scanning apparatus and a control method thereof.
2. Description of the Related Art
A technique for controlling the moving speed of an optical system in an original scanning apparatus is known. Japanese Patent Laid-Open No. 05-199375 discloses a technique in which, when scanning an original, a strip-shaped pattern formed on the contact glass is detected by a solid-state image sensor, and the position and speed of the optical system is controlled based on the detected strip-shaped pattern.
According to Japanese Patent Laid-Open No. 05-199375, the strip-shaped pattern is formed on the contact glass so that the brightness information changes at a regular interval in the sub-scanning direction of the solid-state image sensor, and a plurality of types of strip-shaped patterns that have different pitches are prepared to cope with different linear speeds. The solid-state image sensor outputs one line's worth of signal in a prescribed cycle.
In the above-described technique, the strip-shaped pattern is scanned by the solid-state image sensor. Accordingly, the scan timing of the strip-shaped pattern is limited to the scan timing of the solid-state image sensor, so it is difficult to obtain highly precise information regarding the position and speed of the optical system.
To obtain highly precise information, it is necessary to obtain precise information regarding a black/white border point of the strip-shaped pattern. To obtain such information regarding a black/white border point of the strip-shaped pattern, it is necessary to sufficiently lower the line-scanning speed of the solid-state image sensor with respect to the moving speed of the optical system. However, since there is a limit on how much the speed of the light-receiving can be increased, there is no way but to slow down the moving speed of the optical system.
Also, with the above-described technique, in order to cope with scan modes of different linear speeds, it is necessary to prepare a plurality of strip-shaped patterns that have different pitches.